Transcriptional regulation of the gene encoding the cyclin dependent protein kinase inhibitor p21 waf1/cip1 is an important focal point for cellular response to cytotoxic stressors, including chemotherapy induced DMA damage. In particular, induced expression of p21 results in the activation of pathways enabling a cell to undergo cell cycle arrest and DNA repair, or alternatively apoptotic cell death. It has become clear that there are both p53 dependent and p53-independent mechanisms regulating the p21 promoter through different protein cascades. Furthermore, since p21 protein can regulate either cell cycle arrest or apoptosis, regulation of p21 basal repression is critical for allowing pathway specific activation. This level of exquisite promoter control is necessary so that mutations or catastrophic mitoses following DNA damage are not propagated and the subsequent risk of carcinoma increased. However, this is also a mal-adaptive mechanism by which tumor metastases including those of prostate and breast cancer may escape currently available chemotherapy and radiation treatments. Mechanisms by which p21 is regulated therefore represent potential targets for mediating directed cell killing or adjuvant therapy to make these metastatic tumors more susceptible to DNA damaging agents. The long term goals of the proposed research are to understand the transcriptional control mechanisms of key genes activated by DNA damage, in particular the control of the p21waf1/cip1 promoter. We have hypothesized a link between DNA damage and the changes in absolute NAD concentrations resulting from poly(ADP)ribose polymerase activation. In particular, we have been studying the effect of NAD on the oligomerization of the transcriptional co-repressor CtBP. The Specific Aims for this project seek to understand the effect of NAD on the co-repressor function of CtBP and the mechanism by which CtBP exerts this co-repressor function on the p21 promoter. We will test hypotheses that CtBP is a conditional co-repressor that responds to alterations in NAD concentrations at the p21 promoter and delineate the biochemical determinants required by CtBP for mediating its co-repressor function.